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I am planning to upgrade my Dell PRECISION M4300 laptop with an SSD, using the current HDD as mass storage /dev/sdb: HDD Model=ST9500420AS, FwRev=0002SDM1 /dev/sda: SSD Model=Samsung SSD 840 Series, FwRev=DXT06B0Q I have a NewModeus optical bay caddy (SATA to IDE) for my Dell. Right now, I test the system with the SSD in the caddy, and the HDD in the main slot. Even if in the end I plan to switch them. My system is Debian Linux 7.0 (Wheezy) I have just found your very informative post and tried the following: I have been using the following setpci in the grub configuration setpci -d 8086:2850 54.l=3033 setpci -d 8086:2850 40.b=5 setpci -d 8086:2850 41.b=A3 setpci -d 8086:2850 43.b=0 setpci -d 8086:2850 48.b=1 setpci -d 8086:2850 4A.b=2 But I still observe the real degradation of speed: # hdparm -t /dev/sdb /dev/sda /dev/sdb: Timing buffered disk reads: 268 MB in 3.00 seconds = 89.19 MB/sec /dev/sda: Timing buffered disk reads: 8 MB in 3.32 seconds = 2.41 MB/sec with a large number of IO error messages in the kernel logfile And then when I check the pci registers from the shell setpci -d 8086:2850 54.l => 2032 setpci -d 8086:2850 40.b => 7 setpci -d 8086:2850 41.b => e3 setpci -d 8086:2850 43.b => 40 setpci -d 8086:2850 48.b => 00 setpci -d 8086:2850 4A.b => 02 My bios is set AHCI, and lspci -nnv give the following … 00:1f.1 IDE interface [0101]: Intel Corporation 82801HM/HEM (ICH8M/ICH8M-E) IDE Controller [8086:2850] (rev 02) (prog-if 8a [Master SecP PriP]) Subsystem: Dell Device [1028:01ff] Flags: bus master, medium devsel, latency 0, IRQ 16 I/O ports at 01f0 I/O ports at 03f4 I/O ports at 0170 I/O ports at 0374 I/O ports at 6fa0 Kernel driver in use: ata_piix 00:1f.2 SATA controller [0106]: Intel Corporation 82801HM/HEM (ICH8M/ICH8M-E) SATA Controller [AHCI mode] [8086:2829] (rev 02) (prog -if 01 [AHCI 1.0]) Subsystem: Dell Device [1028:01ff] Flags: bus master, 66MHz, medium devsel, latency 0, IRQ 45 I/O ports at 6eb0 I/O ports at 6eb8 I/O ports at 6ec0 I/O ports at 6ec8 I/O ports at 6ee0 Memory at f6ffb800 (32-bit, non-prefetchable) Capabilities: [80] MSI: Enable+ Count=1/4 Maskable- 64bit- Capabilities: [70] Power Management version 3 Capabilities: [a8] SATA HBA v1.0 Kernel driver in use: ahci … Looking in the log, the configuration starts nice … [ 1.452610] ata1.00: ATA-9: Samsung SSD 840 Series, DXT06B0Q, max UDMA/133 [ 1.452613] ata1.00: 488397168 sectors, multi 8: LBA48 NCQ (depth 0/1) [ 1.468455] ata1.00: configured for UDMA/100 … but then goes down all the way to [ 132.028769] ata1.00: configured for PIO4 [ 4230.976758] ata1.00: exception Emask 0x0 SAct 0x0 SErr 0x0 action 0x6 [ 4230.976771] ata1.00: failed command: READ MULTIPLE EXT [ 4230.976787] ata1.00: cmd 29/00:00:00:00:00/00:02:00:00:00/e0 tag 0 pio 262144 in [ 4230.976791] res 51/84:f0:10:00:00/84:01:00:00:00/e0 Emask 0x10 (ATA bus error) [ 4230.976799] ata1.00: status: { DRDY ERR } [ 4230.976806] ata1.00: error: { ICRC ABRT } [ 4230.976868] ata1: soft resetting link [ 4231.156645] ata1.00: configured for PIO4 [ 4231.156663] ata1: EH complete [ 4263.992076] ata1.00: exception Emask 0x0 SAct 0x0 SErr 0x0 action 0x6 frozen [ 4263.992082] ata1.00: failed command: READ MULTIPLE … [ 6321.728983] ata3.00: configured for UDMA/133 [ 6321.796683] ata1.00: configured for PIO4 Any hint?